Multipane glazing structures have been in use for some time as thermally insulating windows, in residential, commercial and industrial contexts. Examples of such structures may be found in U.S. Pat. Nos. 3,499,697, 3,523,847 and 3,630,809 to Edwards, 4,242,386 to Weinlich, 4,520,611 to Shingu et al., and 4,639,069 to Yatabe et al. While each of these patents relates to laminated glazing structures which provide better insulation performance than single-pane windows, increasing energy costs as well as demand for a superior product have given rise to a need for windows of even higher thermal insulation ability.
A number of different kinds of approaches have been taken to increase the thermal insulation performance of windows. Additional panes have been incorporated into a laminated structure, as disclosed in several of the above-cited patents; typically, incorporation of additional panes will increase the R-value of the structure from R-1 for a single-pane window to R-2 for a double laminate, to R-3 for a structure which includes 3 or more panes (with "R-values" defined according to the insulation resistance test set forth by the American Society for Testing and Materials in the Annual Book of ASTM Standards). Southwall Technologies Inc., the assignee of the present invention, has promoted such a triple-glazing structure which employs two glass panes containing an intermediate plastic film. Such products are described, for example, in U.S. Pat. No. 4,335,166 to Lizardo et al.
In addition, heat-reflective, low-emissivity ("low e") coatings have been incorporated into one or more panes of a window structure, increasing the R-value to 3.5 or higher. Such a heat-reflective coating is described, for example, in U.S. Pat. No. 4,337,990 to Fan et al. (which discloses coating of a plastic film with dielectric/metal/dielectric induced transmission filter layers). Window structures which include heat-reflective coatings are described in U.S. Pat. Nos. 3,978,273 to Groth, 4,413,877 to Suzuki et al., 4,536,998 to Matteucci et al., and 4,579,638 to Scherber.
Still another and more recent method which has been developed for increasing the thermal insulation performance of windows is the incorporation, into the window structure, of a low heat transfer gas such as sulfur hexafluoride (as described in U.S. Pat. No. 4,369,084 to Lisec), argon (as described in U.S. Pat. Nos. 4,393,105 to Kreisman and 4,756,783 to McShane), or krypton (also as disclosed in McShane '783). These gas-filled laminated windows are reported to have total window R-values of 4 or 5, with the total window R-value approximating the average of the center-of-glass and edge area R-values (Arasteh, "Superwindows., in Glass Magazine, May 1989, at pages 82-83).
Despite the increasing complexity in the design of insulating window structures, total window R-values have not surpassed 4 or 5. While not wishing to be bound by theory, the inventors herein postulate several reasons for the limited insulating performance of prior art window structures: (1) thermal conductance across interpane metal spacers present at the window edge; (2) thermal conductance within and across the edge sealant; and (3) the impracticality, due to considerations of window weight and thickness, of having a large number of panes in a single glazing structure.
The present invention addresses each of the aforementioned problems and thus provides a novel multipane window structure of exceptionally high thermal insulating performance.
In addition to insulating performance, the following characteristics are extremely desirable in a window structure and are provided by the present invention as well:
durability under extremes of temperature; PA1 resistance of internal metallized films to yellowing; PA1 resistance to condensation, even at very low temperatures; PA1 low ultraviolet transmission; and PA1 good acoustical performance, i.e., sound deadening within the multilaminate structure.